1. Field of the Invention
The present invention relates to a sheet processing apparatus and an image forming apparatus, and more particularly, to a sheet processing apparatus and an image forming apparatus which are configured to bind sheets with use of a binding unit of different types.
2. Description of the Related Art
Hitherto, image forming apparatus such as copying machines, laser beam printers, fax machines and multifunctional peripherals have included a sheet processing apparatus configured to bind sheets. In such a sheet processing apparatus, a sheet bundle, including a plurality of sheets, is bound using a metal staple. Such a stapling process can reliably bind a plurality of output sheets at a position specified by a user, and hence this process is adopted in many sheet processing apparatus.
Further, in conventional sheet processing apparatus, there has been proposed an apparatus including, in addition to the binding unit using a staple, a binding unit configured to simply bind the sheets without using a staple, on the presumption that “unbinding” of the sheet bundle is to be performed after the binding (see Japanese Patent Application Laid-Open No. 2000-318918). This apparatus includes, in addition to the staple binding unit configured to fasten a maximum of 50 sheets by a staple, a binding unit, as an example of staple-less binding unit, configured to perform simple binding of up to about 10 sheets by forming a half-blanking shaped fastening portion in a sheet bundle. When binding is to be performed in such a sheet processing apparatus, a selective moving mechanism selectively moves each of the binding unit arranged to be movable forward and backward to a binding position of the sheet bundle.
Such a conventional sheet processing apparatus includes the selective moving mechanism for selectively moving each binding unit to the binding position, and hence the configuration of the apparatus becomes complicated. In order to prevent this, the following configurations may be considered. For example, at least the staple-less binding unit is fixed to eliminate the selective moving mechanism.
By the way, when the maximum number of bindable sheets differs between the respective binding units as described above, generally, the height (width in an up-down direction) of a sheet receiving portion (hereinafter referred to as “opening”) opened in the thickness direction of the sheet bundle also differs depending on the maximum number of bindable sheets. Therefore, depending on the fixing positions at which the respective binding units are fixed and depending on the thickness of the sheet bundle when the binding is performed with, for example, the staple binding unit having a larger opening height (a larger maximum number of bindable sheets), the sheet bundle interferes with the staple-less binding unit having a smaller opening height (a smaller maximum number of bindable sheets).